1. Field of the Invention
The present invention relates to a bow and more particularly to a western style bow that has string grooves for accommodating the bowstring.
2. Prior Art
FIG. 6 shows one of conventional western style bows.
In this bow, the main body 1 of the bow is made of a handle 2 and upper and lower limbs 3 which are detachable from the handle 2. A bowstring S is strung between the tip ends 4a of the upper and lower limbs 3. A string groove 6, as shown in FIGS. 7 and 8, is formed for a prescribed length L in the end portion of each one of the limbs 3. The groove 6 is ordinarily 70.0 to 120.0 mm long, and it runs along the central axis O--O of the limb 3 from the tip end 4a to the root end 4b. In other words, the grooves in the upper and lower limbs are provided in the areas where the bowstring S contacts the face 3a of the recurve 5 of the limb 3 when the bowstring is strung on the bow.
The string grooves 6 are provided, as shown in FIGS. 9 and 10, so that the bowstring S is brought back on the central axis O--O of the limbs 3 after being released from a drawn state when an arrow is launched. With these string grooves in the upper and lower limbs, the direction of the launched arrow is stabilized, and the percentage of arrows striking the target is improved.
However, the width dimension W (see FIG. 9) of each of the string grooves 6 of this type of bow is uniform for the entire length within the range of 4.0 to 5.0 mm long as opposed to the bowstring thickness (or diameter) of 2.2 to 2.6 mm that includes the protective layer of a reinforced bowstring. Furthermore, the depth D of the string groove 6 is set to be the same for the entire length so that it is 0.8 to 1.3 mm deep, which is shallower than the thickness of the bowstring S. As a result, the accommodation ratio of the bowstring S into the groove 6 after launching is poor.
In the meantime, in an ideal full drawing of the bowstring, as shown in FIG. 11, the center line p--p of the shoulders of the archer P is parallel to the arrow launch direction X. However, when this parallel relationship is lost, several problems occur. More specifically, when the bowstring is released with the center line p--p of the shoulders not parallel to the arrow launch direction X as a result of the pushing hand of the archer P extending too far outward as shown in FIG. 12 or as a result of the elbow of the pulling hand of the archer P extending too far forward as shown in FIG. 13, the limbs 3 tend to recover in a twisted state. Accordingly, the bowstring S recovering with the limbs 3 strikes the face 3a of the limb 3 and does not enter the string grooves 6; in other words, an accurate accommodation of the bowstring S back into the string grooves 6 is not obtained. This disenables the quick and accurate recovery of the bowstring S to the central axis O--O of the limbs 3.
If arrows are repeatedly launched with the limbs 3 under such a twisted condition, twisting deformation can remain in the limbs 3 permanently, and the mutual discrepancy in the recovery of the limbs 3 and bowstring S at the time of release causes an inaccurate return of the bowstring S to the central axis O--O of the limbs 3. As a result, the arrow launch direction X at the time of releasing the arrow becomes skewed, creating a constant error in the left-right direction and decreasing the percentage of arrows striking the target.
Furthermore, some bows use limbs that are of a sandwich or laminated structure. In these types of sandwich-structured limbs, as shown in FIG. 10, FRP (fiber reinforced plastics) layers 32, that use glass fibers, carbon fibers, etc., as reinforcing fibers, are laminated on the front and back surfaces of a wooden core 31, and the string grooves 6 are formed by cutting into the FRP layer 32. When the FRP layers are thus cut for forming the grooves, chances are that the reinforcing fibers in the FRP layer 32 on the face 3a side of the limb would be cut into.
Such cutting of the reinforcing fibers in the FRP layers 32 of the limbs 3 causes a drop in the bending and twisting rigidity and a strength decrease in the limbs 3, and it is also extremely dangerous. Splitting, etc. would occur in the groove-worked areas of the string grooves 6. In order to avoid such damages, the depth D of the string grooves 6 is inevitably limited, and deep string grooves are not able to be created.